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Refining the Dispersion Relation

Due to discontinuities in the line detections as well as in the calibration process, the dispersion relations computed by the row-by-row process could show row-to-row discontinuous variations. The command CALIBRATE/TWICE, provided that a sufficient number of calibration lines is available, can stabilize the solutions by performing a two-pass wavelength calibration which retains for the second pass only the lines that were consistently identified during the first pass.

Petra Nass